Short-term effects of alcohol
Encyclopedia
Short-term effects of alcohol on the human body can take many forms. The drug
alcohol
, to be specific ethanol
, is a central nervous system
depressant
with a range of side-effects
. The amount and circumstances of consumption play a large part in determining the extent of intoxication; for example, consuming alcohol after a heavy meal causes alcohol to absorb more slowly. Hydration
also plays a role, especially in determining the extent of hangover
s. The concentration of alcohol in blood is usually measured in terms of the blood alcohol content
. Cell membrane
s are highly permeable to alcohol, so once alcohol is in the bloodstream it can diffuse into nearly every biological tissue of the body. After excessive drinking
, unconsciousness
can occur and extreme levels of consumption can lead to alcohol poisoning and death (a concentration in the blood stream of 0.40% will kill half of those affected). Death can also occur through asphyxiation by vomit.
Alcohol
is an addictive drug that can greatly exacerbate sleep problems. During abstinence
, residual disruptions in sleep regularity and sleep patterns are the greatest predictors of relapse
.
, disrupts sleep architecture. Rebound effects occur once the alcohol has been largely metabolized, causing late night disruptions in sleep maintenance. Under conditions of moderate alcohol consumption where blood alcohol levels average 0.06–0.08 percent and decrease 0.01–0.02 percent per hour, an alcohol clearance rate of 4–5 hours would coincide with disruptions in sleep maintenance in the second half of an 8 hour sleep episode. In terms of sleep architecture, moderate doses of alcohol facilitate "rebounds" in rapid eye movement (REM) and stage 1 sleep; following suppression in REM and stage 1 sleep in the first half of an 8 hour sleep episode, REM and stage 1 sleep increase well beyond baseline in the second half. Moderate doses of alcohol also very quickly increase slow wave sleep (SWS) in the first half of an 8 hour sleep episode. Enhancements in REM sleep and SWS following moderate alcohol consumption are mediated by reductions in glutamatergic activity by adenosine in the central nervous system
. In addition, tolerance to changes in sleep maintenance and sleep architecture develops within 3 days of alcohol consumption before bedtime.
) increase total sleep time and reduce awakening during the night. The sleep-promoting benefits of alcohol dissipate at moderate and higher doses of alcohol. Previous experience with alcohol also influences the extent to which alcohol positively or negatively affects sleep. Under free-choice conditions, in which subjects chose between drinking alcohol or water, inexperienced drinkers were sedated while experienced drinkers were stimulated following alcohol consumption. In insomnia
cs, moderate doses of alcohol improve sleep maintenance.
correlate positively with increased alcohol consumption. In Northern climates, increased alcohol consumption during the winter months is attributed to escalations in fatigue.
secretion at onset of a sleep episode, resulting in prolonged sleep onset latencies. Escalations in cortisol
and core body temperatures during the sleep period contribute to poor sleep maintenance.
The following lists the common effects of alcohol on the body, depending on the blood alcohol concentration (BAC). However, tolerance varies considerably between individuals, as does individual response to a given dosage; the effects of alcohol differ widely between people. Hence, BAC percentages are just estimates used for illustrative purposes.
Euphoria (BAC = 0.03 to 0.12%):
Lethargy (BAC = 0.09 to 0.25%)
Confusion (BAC = 0.18 to 0.30%)
Stupor (BAC = 0.25 to 0.40%)
Coma (BAC = 0.35 to 0.50%)
) subtype of glutamate receptors. Stimulated areas include the cortex, hippocampus
and nucleus accumbens
, which are responsible for thinking and pleasure seeking. Another one of alcohol's agreeable effects is body relaxation, possibly caused by neurons transmitting electrical signals in an alpha waves
-pattern; such waves are observed (with the aid of EEG
s) when the body is relaxed.
Short-term effects of alcohol include the risk of injuries, violence and fetal damage. Alcohol has also been linked with lowered inhibitions, though it is unclear to what degree this is chemical versus psychological as studies with placebo
s can often duplicate the social effects of alcohol at low to moderate doses. Some studies have suggested that intoxicated people have much greater control over their behavior than is generally recognized, though they have a reduced ability to evaluate the consequences of their behavior. Behavioral changes associated with drunkenness are, to some degree, contextual. A scientific study found that people drinking in a social setting significantly and dramatically altered their behavior immediately after the first sip of alcohol, well before the chemical itself could have filtered through to the nervous system.
Areas of the brain responsible for planning and motor learning are dulled. A related effect, caused by even low levels of alcohol, is the tendency for people to become more animated in speech and movement. This is due to increased metabolism
in areas of the brain associated with movement, such as the nigrostriatal pathway
. This causes reward systems in the brain to become more active, which may induce certain individuals to behave in an uncharacteristically loud and cheerful manner.
Alcohol has been known to mitigate the production of antidiuretic hormone (ADH), which is a hormone that acts on the kidney, favoring water reabsorption in the kidneys during filtration. This occurs because alcohol confuses osmoreceptor
s in the hypothalamus
, which relay osmotic pressure
information to the posterior pituitary
, the site of ADH release. Alcohol causes the osmoreceptors to signal that there is low osmotic pressure in the blood, which triggers an inhibition of ADH. As a consequence, one's kidneys are no longer able to reabsorb as much water as they should be absorbing, leading to creation of excessive volumes of urine and the subsequent overall dehydration.
receptors start to become unresponsive, slowing areas of the brain for which they are responsible. Contributing to this effect is the activity that alcohol induces in the gamma-aminobutyric acid
(GABA) system. The GABA system is known to inhibit activity in the brain. GABA could also be responsible for the memory impairment that many people experience. It has been asserted that GABA signals interfere with the registration and consolidation stages of memory formation. As the GABA system is found in the hippocampus (among other areas in the CNS), which is thought to play a large role in memory formation, this is thought to be possible.
Anterograde amnesia
, colloquially referred to as "blacking out
", is another symptom of heavy drinking. This is the loss of memory during and after an episode of drinking.
Another classic finding of alcohol intoxication is ataxia
, in its appendicular, gait, and truncal forms. Appendicular ataxia results in jerky, uncoordinated movements of the limbs, as though each muscle were working independently from the others. Truncal ataxia results in postural instability; gait instability is manifested as a disorderly, wide-based gait with inconsistent foot positioning. Ataxia is responsible for the observation that drunk people are clumsy, sway back and forth, and often fall down. It is presumed to be due to alcohol's effect on the cerebellum
.
Alcohol has a powerful effect on glutamate as well. Alcohol decreases glutamate's ability to bind with NMDA and acts as an antagonist of the NMDA receptor
, which plays a critical role in LTP
by allowing Ca2+ to enter the cell. These inhibitory effects are thought to be responsible for the "memory blanks" that can occur at levels as low as 0.03% blood level. In addition, reduced glutamate release in the dorsal hippocampus has been linked to spatial memory loss.
Chronic alcohol users experience an upregulation of NMDA receptors because the brain is attempting to reestablish homeostasis
. When a chronic alcohol user stops drinking for more than 10 hours, apoptosis can occur due to excitotoxicity
. The seizures experienced during alcohol abstinence are thought to be a result of this NMDA upregulation. Alteration of NMDA receptor numbers in chronic alcoholics is likely to be responsible for some of the symptoms seen in delirium tremens
during severe alcohol withdrawal, such as delirium and hallucinations. Other targets such as sodium channels can also be affected by high doses of alcohol, and alteration in the numbers of these channels in chronic alcoholics is likely to be responsible for as well as other effects such as cardiac arrhythmia.
Other targets that are affected by alcohol include cannabinoid, opioid and dopamine receptors, although it is unclear whether alcohol affects these directly or if they are affected by downstream consequences of the GABA/NMDA effects.
People with a family history of alcoholism may exhibit genetic differences in the response of their NMDA glutamate receptors as well as the ratios of GABA-A subtypes in their brain.
More recently, studies using animal models have begun to elucidate the effects of ethanol on the nervous system. Traditionally, many studies have been performed in mammals, such as mice, rats, and non-human primates. However, non-mammalian animal models have also been employed; in particular, Ulrike Heberlein group at UC San Francisco has used Drosophila melanogaster
, the fruit fly, taking advantage of its facile genetics to dissect the neural circuits and molecular pathways, upon which ethanol acts. The series of studies carried in the Heberlein lab has identified insulin and its related signaling pathways as well as biogenic amines in the invertebrate nervous system as being important in alcohol tolerance. The value of antabuse (disulfiram) as a treatment for alcoholism has been tested using another invertebrate animal model, the honey bees.
It is important to note that some of the analogous biochemical pathways and neural systems have been known to be important in alcohol's effects on humans, while the possibility that others may also be important remains unknown. Research of alcohol's effects on the nervous system remains a hot topic of research, as scientists inch toward understanding the problem of alcohol addiction.
In addition to the studies carried out in invertebrates, researchers have also used vertebrate animal models to study various effects of ethanol on behaviors.
Drug
A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...
alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
, to be specific ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
, is a central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
depressant
Depressant
A depressant, or central depressant, is a drug or endogenous compound that depresses the function or activity of a specific part of the brain...
with a range of side-effects
Adverse effect
In medicine, an adverse effect is a harmful and undesired effect resulting from a medication or other intervention such as surgery.An adverse effect may be termed a "side effect", when judged to be secondary to a main or therapeutic effect. If it results from an unsuitable or incorrect dosage or...
. The amount and circumstances of consumption play a large part in determining the extent of intoxication; for example, consuming alcohol after a heavy meal causes alcohol to absorb more slowly. Hydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
also plays a role, especially in determining the extent of hangover
Hangover
A hangover describes the sum of unpleasant physiological effects following heavy consumption of alcoholic beverages. The most commonly reported characteristics of a hangover include headache, nausea, sensitivity to light and noise, lethargy, dysphoria, diarrhea and thirst, typically after the...
s. The concentration of alcohol in blood is usually measured in terms of the blood alcohol content
Blood alcohol content
Blood alcohol content , also called blood alcohol concentration, blood ethanol concentration, or blood alcohol level is most commonly used as a metric of alcohol intoxication for legal or medical purposes....
. Cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
s are highly permeable to alcohol, so once alcohol is in the bloodstream it can diffuse into nearly every biological tissue of the body. After excessive drinking
Binge drinking
Binge drinking or heavy episodic drinking is the modern epithet for drinking alcoholic beverages with the primary intention of becoming intoxicated by heavy consumption of alcohol over a short period of time. It is a kind of purposeful drinking style that is popular in several countries worldwide,...
, unconsciousness
Unconsciousness
Unconsciousness is the condition of being not conscious—in a mental state that involves complete or near-complete lack of responsiveness to people and other environmental stimuli. Being in a comatose state or coma is a type of unconsciousness. Fainting due to a drop in blood pressure and a...
can occur and extreme levels of consumption can lead to alcohol poisoning and death (a concentration in the blood stream of 0.40% will kill half of those affected). Death can also occur through asphyxiation by vomit.
Alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
is an addictive drug that can greatly exacerbate sleep problems. During abstinence
Abstinence
Abstinence is a voluntary restraint from indulging in bodily activities that are widely experienced as giving pleasure. Most frequently, the term refers to sexual abstinence, or abstention from alcohol or food. The practice can arise from religious prohibitions or practical...
, residual disruptions in sleep regularity and sleep patterns are the greatest predictors of relapse
Relapse
Relapse, in relation to drug misuse, is resuming the use of a drug or a dependent substance after one or more periods of abstinence. The term is a landmark feature of both substance dependence and substance abuse, which are learned behaviors, and is maintained by neuronal adaptations that mediate...
.
Moderate alcohol consumption and sleep disruptions
Moderate alcohol consumption 30–60 minutes before sleep, although decreasing sleep onset latencySleep onset latency
In sleep science, sleep onset latency is the length of time that it takes to accomplish the transition from full wakefulness to sleep, normally to the lightest of the non-REM sleep stages.-Sleep latency studies:...
, disrupts sleep architecture. Rebound effects occur once the alcohol has been largely metabolized, causing late night disruptions in sleep maintenance. Under conditions of moderate alcohol consumption where blood alcohol levels average 0.06–0.08 percent and decrease 0.01–0.02 percent per hour, an alcohol clearance rate of 4–5 hours would coincide with disruptions in sleep maintenance in the second half of an 8 hour sleep episode. In terms of sleep architecture, moderate doses of alcohol facilitate "rebounds" in rapid eye movement (REM) and stage 1 sleep; following suppression in REM and stage 1 sleep in the first half of an 8 hour sleep episode, REM and stage 1 sleep increase well beyond baseline in the second half. Moderate doses of alcohol also very quickly increase slow wave sleep (SWS) in the first half of an 8 hour sleep episode. Enhancements in REM sleep and SWS following moderate alcohol consumption are mediated by reductions in glutamatergic activity by adenosine in the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
. In addition, tolerance to changes in sleep maintenance and sleep architecture develops within 3 days of alcohol consumption before bedtime.
Alcohol consumption and sleep improvements
Low doses of alcohol (one 360 ml (3.240032400324E-08 imp fl oz) beerBeer
Beer is the world's most widely consumed andprobably oldest alcoholic beverage; it is the third most popular drink overall, after water and tea. It is produced by the brewing and fermentation of sugars, mainly derived from malted cereal grains, most commonly malted barley and malted wheat...
) increase total sleep time and reduce awakening during the night. The sleep-promoting benefits of alcohol dissipate at moderate and higher doses of alcohol. Previous experience with alcohol also influences the extent to which alcohol positively or negatively affects sleep. Under free-choice conditions, in which subjects chose between drinking alcohol or water, inexperienced drinkers were sedated while experienced drinkers were stimulated following alcohol consumption. In insomnia
Insomnia
Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...
cs, moderate doses of alcohol improve sleep maintenance.
Alcohol consumption and fatigue
Conditions of sleep deprivationSleep deprivation
Sleep deprivation is the condition of not having enough sleep; it can be either chronic or acute. A chronic sleep-restricted state can cause fatigue, daytime sleepiness, clumsiness and weight loss or weight gain. It adversely affects the brain and cognitive function. Few studies have compared the...
correlate positively with increased alcohol consumption. In Northern climates, increased alcohol consumption during the winter months is attributed to escalations in fatigue.
Alcohol abstinence and sleep disruptions
Hormonal imbalance and sleep disruption following withdrawal from chronic alcohol consumption are strong predictors of relapse. During abstinence, recovering alcoholics have attenuated melatoninMelatonin
Melatonin , also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes...
secretion at onset of a sleep episode, resulting in prolonged sleep onset latencies. Escalations in cortisol
Cortisol
Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...
and core body temperatures during the sleep period contribute to poor sleep maintenance.
Effects by dosage
Different concentrations of alcohol in the human body have different effects on the subject.The following lists the common effects of alcohol on the body, depending on the blood alcohol concentration (BAC). However, tolerance varies considerably between individuals, as does individual response to a given dosage; the effects of alcohol differ widely between people. Hence, BAC percentages are just estimates used for illustrative purposes.
Euphoria (BAC = 0.03 to 0.12%):
- Overall improvement in mood and possible euphoriaEuphoriaEuphoria is an emotional and mental state defined as a sense of great elation and well being.Euphoria may also refer to:* Euphoria , a genus of scarab beetles* Euphoria, a genus name previously used for the longan and other trees...
- Increased self-confidence
- Increased sociability
- Shortened attention span
- Flushed appearanceAlcohol flush reactionAlcohol flush reaction or Oriental Flushing Syndrome is a condition in which the face and/or body experiences flushes or blotches, due to an accumulation of acetaldehyde...
- Impaired judgment
- Impaired fine muscle coordination
Lethargy (BAC = 0.09 to 0.25%)
- Sedation
- Impaired memory and comprehension
- Delayed reactions
- AtaxiaAtaxiaAtaxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...
; balance difficulty; unbalanced walk - Blurred vision; other senses may be impaired
Confusion (BAC = 0.18 to 0.30%)
- Profound confusion
- Emotional lability
- Impaired senses
- Analgesia
- Increased ataxia; impaired speech; staggering
- Dizziness often associated with nauseaNauseaNausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
("the spins") - Vomiting (emesis)
Stupor (BAC = 0.25 to 0.40%)
- Severe ataxia
- Lapses in and out of consciousness
- Unconsciousness
- Anterograde amnesiaAnterograde amnesiaAnterograde amnesia is a loss of the ability to create new memories after the event that caused the amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact. This is in contrast to retrograde amnesia, where memories...
- Vomiting (death may occur due to inhalation of vomit (pulmonary aspirationPulmonary aspirationPulmonary aspiration is the entry of material from the oropharynx or gastrointestinal tract into the larynx and lower respiratory tract...
) while unconscious) - Respiratory depression (potentially life-threatening)
- Decreased heart rateHeart rateHeart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
- Urinary incontinenceUrinary incontinenceUrinary incontinence is any involuntary leakage of urine. It is a common and distressing problem, which may have a profound impact on quality of life. Urinary incontinence almost always results from an underlying treatable medical condition but is under-reported to medical practitioners...
Coma (BAC = 0.35 to 0.50%)
- Unconsciousness (comaComaIn medicine, a coma is a state of unconsciousness, lasting more than 6 hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light or sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions. A person in a state of coma is described as...
) - Depressed reflexes (i.e., pupils do not respond appropriately to changes in light)
- Marked and life-threatening respiratory depression
- Markedly decreased heart rate
- Most deaths from alcohol poisoning are caused by dosage levels in this range.
Moderate doses
Ethanol inhibits the ability of glutamate to open the cation channel associated with the N-methyl-D-aspartate (NMDANMDA
N-Methyl-D-aspartic acid or N-Methyl-D-aspartate is an amino acid derivative which acts as a specific agonist at the NMDA receptor mimicking the action of glutamate, the neurotransmitter which normally acts at that receptor...
) subtype of glutamate receptors. Stimulated areas include the cortex, hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
and nucleus accumbens
Nucleus accumbens
The nucleus accumbens , also known as the accumbens nucleus or as the nucleus accumbens septi , is a collection of neurons and forms the main part of the ventral striatum...
, which are responsible for thinking and pleasure seeking. Another one of alcohol's agreeable effects is body relaxation, possibly caused by neurons transmitting electrical signals in an alpha waves
Alpha Waves
Alpha Waves is an early 3D game that combines labyrinthine exploration with platform gameplay. By most definitions of the genre it could be considered to be the first 3D platform game, released in 1990, 6 years before the genre's seminal classic Super Mario 64...
-pattern; such waves are observed (with the aid of EEG
EEG
EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...
s) when the body is relaxed.
Short-term effects of alcohol include the risk of injuries, violence and fetal damage. Alcohol has also been linked with lowered inhibitions, though it is unclear to what degree this is chemical versus psychological as studies with placebo
Placebo
A placebo is a simulated or otherwise medically ineffectual treatment for a disease or other medical condition intended to deceive the recipient...
s can often duplicate the social effects of alcohol at low to moderate doses. Some studies have suggested that intoxicated people have much greater control over their behavior than is generally recognized, though they have a reduced ability to evaluate the consequences of their behavior. Behavioral changes associated with drunkenness are, to some degree, contextual. A scientific study found that people drinking in a social setting significantly and dramatically altered their behavior immediately after the first sip of alcohol, well before the chemical itself could have filtered through to the nervous system.
Areas of the brain responsible for planning and motor learning are dulled. A related effect, caused by even low levels of alcohol, is the tendency for people to become more animated in speech and movement. This is due to increased metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
in areas of the brain associated with movement, such as the nigrostriatal pathway
Dopaminergic pathways
Dopaminergic pathways are neural pathways in the brain which transmit the neurotransmitter dopamine from one region of the brain to another.The neurons of the dopaminergic pathways have axons which run the entire length of the pathway...
. This causes reward systems in the brain to become more active, which may induce certain individuals to behave in an uncharacteristically loud and cheerful manner.
Alcohol has been known to mitigate the production of antidiuretic hormone (ADH), which is a hormone that acts on the kidney, favoring water reabsorption in the kidneys during filtration. This occurs because alcohol confuses osmoreceptor
Osmoreceptor
An osmoreceptor is a sensory receptor primarily found in the hypothalamus of most homeothermic organisms that detects changes in osmotic pressure. Osmoreceptors can be found in several structures, including the organum vasculosum of the lamina terminalis and the subfornical organ...
s in the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
, which relay osmotic pressure
Osmotic pressure
Osmotic pressure is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane....
information to the posterior pituitary
Posterior pituitary
The posterior pituitary comprises the posterior lobe of the pituitary gland and is part of the endocrine system. Despite its name, the posterior pituitary gland is not a gland, per se; rather, it is largely a collection of axonal projections from the hypothalamus that terminate behind the anterior...
, the site of ADH release. Alcohol causes the osmoreceptors to signal that there is low osmotic pressure in the blood, which triggers an inhibition of ADH. As a consequence, one's kidneys are no longer able to reabsorb as much water as they should be absorbing, leading to creation of excessive volumes of urine and the subsequent overall dehydration.
Excessive doses
Acute alcohol intoxication via excessive doses in general causes short- or long-term health effects. NMDANMDA
N-Methyl-D-aspartic acid or N-Methyl-D-aspartate is an amino acid derivative which acts as a specific agonist at the NMDA receptor mimicking the action of glutamate, the neurotransmitter which normally acts at that receptor...
receptors start to become unresponsive, slowing areas of the brain for which they are responsible. Contributing to this effect is the activity that alcohol induces in the gamma-aminobutyric acid
Gamma-aminobutyric acid
γ-Aminobutyric acid is the chief inhibitory neurotransmitter in the mammalian central nervous system. It plays a role in regulating neuronal excitability throughout the nervous system...
(GABA) system. The GABA system is known to inhibit activity in the brain. GABA could also be responsible for the memory impairment that many people experience. It has been asserted that GABA signals interfere with the registration and consolidation stages of memory formation. As the GABA system is found in the hippocampus (among other areas in the CNS), which is thought to play a large role in memory formation, this is thought to be possible.
Anterograde amnesia
Anterograde amnesia
Anterograde amnesia is a loss of the ability to create new memories after the event that caused the amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact. This is in contrast to retrograde amnesia, where memories...
, colloquially referred to as "blacking out
Blackout (alcohol-related amnesia)
A blackout is a phenomenon caused by the intake of alcohol or other substance in which long term memory creation is impaired or there is a complete inability to recall the past. Blackouts are frequently described as having effects similar to that of anterograde amnesia, in which the subject cannot...
", is another symptom of heavy drinking. This is the loss of memory during and after an episode of drinking.
Another classic finding of alcohol intoxication is ataxia
Ataxia
Ataxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...
, in its appendicular, gait, and truncal forms. Appendicular ataxia results in jerky, uncoordinated movements of the limbs, as though each muscle were working independently from the others. Truncal ataxia results in postural instability; gait instability is manifested as a disorderly, wide-based gait with inconsistent foot positioning. Ataxia is responsible for the observation that drunk people are clumsy, sway back and forth, and often fall down. It is presumed to be due to alcohol's effect on the cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
.
Pathophysiology
At low or moderate doses, alcohol acts primarily as a positive allosteric modulator of GABAA. Alcohol binds to several different subtypes of GABAA, but not to others. The main subtypes responsible for the subjective effects of alcohol are the α1β3γ2, α5β3γ2, α4β3δ and α6β3δ subtypes, although other subtypes such as α2β3γ2 and α3β3γ2 are also affected. Activation of these receptors causes most of the effects of alcohol such as relaxation and relief from anxiety, sedation, ataxia and increase in appetite and lowering of inhibitions that can cause a tendency toward violence in some people.Alcohol has a powerful effect on glutamate as well. Alcohol decreases glutamate's ability to bind with NMDA and acts as an antagonist of the NMDA receptor
NMDA receptor
The NMDA receptor , a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function....
, which plays a critical role in LTP
LTP
- Science and technology :* Lunar Transient Phenomena, a short-lived change in appearance of Earth's moon* Long-tailed pair, a differential pair amplifier* Lightweight Telephony Protocol, a signaling protocol...
by allowing Ca2+ to enter the cell. These inhibitory effects are thought to be responsible for the "memory blanks" that can occur at levels as low as 0.03% blood level. In addition, reduced glutamate release in the dorsal hippocampus has been linked to spatial memory loss.
Chronic alcohol users experience an upregulation of NMDA receptors because the brain is attempting to reestablish homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
. When a chronic alcohol user stops drinking for more than 10 hours, apoptosis can occur due to excitotoxicity
Excitotoxicity
Excitotoxicity is the pathological process by which nerve cells are damaged and killed by excessive stimulation by neurotransmitters such as glutamate and similar substances. This occurs when receptors for the excitatory neurotransmitter glutamate such as the NMDA receptor and AMPA receptor are...
. The seizures experienced during alcohol abstinence are thought to be a result of this NMDA upregulation. Alteration of NMDA receptor numbers in chronic alcoholics is likely to be responsible for some of the symptoms seen in delirium tremens
Delirium tremens
Delirium tremens is an acute episode of delirium that is usually caused by withdrawal from alcohol, first described in 1813...
during severe alcohol withdrawal, such as delirium and hallucinations. Other targets such as sodium channels can also be affected by high doses of alcohol, and alteration in the numbers of these channels in chronic alcoholics is likely to be responsible for as well as other effects such as cardiac arrhythmia.
Other targets that are affected by alcohol include cannabinoid, opioid and dopamine receptors, although it is unclear whether alcohol affects these directly or if they are affected by downstream consequences of the GABA/NMDA effects.
People with a family history of alcoholism may exhibit genetic differences in the response of their NMDA glutamate receptors as well as the ratios of GABA-A subtypes in their brain.
Research
Animal models using mammals and invertebrates have been informative in studying the effects of ethanol on not only pharmacokinetics of alcohol but also pharmacodynamics, in particular in the nervous system. Ethanol-induced intoxication is not uncommon in the animal kingdom, as noted here:More recently, studies using animal models have begun to elucidate the effects of ethanol on the nervous system. Traditionally, many studies have been performed in mammals, such as mice, rats, and non-human primates. However, non-mammalian animal models have also been employed; in particular, Ulrike Heberlein group at UC San Francisco has used Drosophila melanogaster
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
, the fruit fly, taking advantage of its facile genetics to dissect the neural circuits and molecular pathways, upon which ethanol acts. The series of studies carried in the Heberlein lab has identified insulin and its related signaling pathways as well as biogenic amines in the invertebrate nervous system as being important in alcohol tolerance. The value of antabuse (disulfiram) as a treatment for alcoholism has been tested using another invertebrate animal model, the honey bees.
It is important to note that some of the analogous biochemical pathways and neural systems have been known to be important in alcohol's effects on humans, while the possibility that others may also be important remains unknown. Research of alcohol's effects on the nervous system remains a hot topic of research, as scientists inch toward understanding the problem of alcohol addiction.
In addition to the studies carried out in invertebrates, researchers have also used vertebrate animal models to study various effects of ethanol on behaviors.
External links
- Global Status Report on Alcohol 2004 by the World Health OrganizationWorld Health OrganizationThe World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
. - Jane behaving badly (New Scientist article on short-term effects of alcohol)